1. Field of the Invention
The present invention relates to an organic electroluminescence (hereinafter referred to as “EL”) display device, and, in particular, to an organic electroluminescence display device having a high reliability in which occurrence of dark spots or the like due to moisture is suppressed.
2. Description of the Related Art
In an organic EL display device, an organic EL layer is sandwiched between a pixel electrode (lower electrode) and an upper electrode, a constant voltage is applied to the upper electrode, and a data signal voltage is applied to the lower electrode, to control light emission of the organic EL layer. And an organic EL display device forms an image. The supply of the data signal voltage to the lower electrode is executed through a thin film transistor (TFT). Organic EL display devices include a bottom-emission type in which the light emitted from the organic EL layer is emitted to a direction toward the glass substrate over which the organic EL layer or the like is formed and a top-emission type in which the light is emitted to a direction opposite to the direction toward the glass substrate over which the organic EL layer or the like is formed.
In the organic EL material which is used for the organic EL display device, the light emission characteristic is degraded when moisture is present. Because of this, when the organic EL display device is operated for a long period of time, locations where the organic EL material is degraded by the moisture stops emitting light. This location appears as a dark spot in the display region. The dark spot grows as time elapses, and becomes a defect of an image. Edge growth which is a phenomenon in which a region where the light is not emitted around the pixel increases is also caused by influence of the moisture.
In order to prevent occurrence or growth of the dark spot or the like, it is necessary to prevent intrusion of moisture into the organic EL display device or to remove the intruded moisture in the organic EL display device. For this purpose, an element substrate over which the organic EL layer is formed is sealed with a sealing substrate via a seal provided at the periphery, so that the intrusion of moisture into the organic EL display device from the outside is prevented. Then, the inside space which is sealed is filled with inert gas such as N2. In addition, in order to remove moisture which entered the organic EL display device, a desiccant is provided within the organic EL display device. Such an organic EL display device is called a hollow-seal organic EL display device.
In a hollow-seal organic EL display device, there are known problems such as that adjustment of the gap between the element substrate and the sealing substrate is difficult, that the adjustment inside the sealed space is difficult, that the organic EL material is contaminated by the gas discharged from the sealing agent when the substrates are sealed with the sealing agent, that the throughput is reduced, etc.
As a countermeasure to the problems of the hollow sealing, there is known a technique in which a resin sheet having a determined thickness is sandwiched between the element substrate and the sealing substrate and the organic EL material is protected from moisture with the resin sheet. This technique is called a solid sealing.
JP 2004-139977 A discloses an example of the solid sealing. FIGS. 18A, 18B, 18C, and 18D show a structure disclosed in JP 2004-139977 A. In FIGS. 18A, 18B, 18C, and 18D, a photo-curing resin 120 which is formed over a light-transmissive film 110 is affixed over an element substrate 10 over which an organic EL layer 22 is provided, using a pressure roller 105 which is heated to a temperature of 80° C. Then, ultraviolet ray is irradiated, to cure the photo-curing resin 120. The light-transmissive film 110 is removed, so that an organic EL display device which is sealed with the photo-curing resin 120 is obtained. In addition, this reference discloses a structure in which the organic EL element is covered with a silicon nitride film as necessary.
An article by Shinya SAEKI, Nikkei Electronics, Sep. 10, 2007, No. 960, pp. 10-11 discloses the following technique for sealing an organic EL display device, as shown in FIGS. 19A, 19B, 19C, 19D, and 19E. A resin film 107 is affixed on a location over a sealing substrate 40 corresponding to the location of an organic EL element 22, and a sealing agent 108 is drawn at the periphery of the resin film 107. The sealing substrate 40 over which the resin film 107 and the sealing agent 108 are formed and an element substrate 10 over which the organic EL element 22 is formed are affixed. Then, ultraviolet ray is irradiated from the side of the sealing substrate 40, and a thermal process of 80° C.-100° C. is applied so that the sealing agent 108 is cured and the resin film 107 now having a flowability spreads in and fills a space formed by the sealing substrate 40, the element substrate 10, and the sealing agent 108. Finally, the structure is divided into individual organic EL display panels. In this manner, an organic EL display panel is completed.
JP 2007-73225 A discloses a structure in which an adhesive member is formed on a flexible sealing member in which a separation region is formed, and this member is adhered to the glass substrate over which a plurality of organic EL elements are formed. JP 2007-73225 A discloses a structure in which, in order to separate only the portion of the flexible sealing member over which the adhesive member is formed and leave this portion over the organic EL display panel, a perforation or a half-cut portion for distinguishing the separation portion and the portion to be removed is formed at a boundary between the separation portion and the portion to be removed.